High-efficiency permanent magnet motor



Sept. 3, 1963 J. L. BENNETT ETAL HIGH-EFFICIENCY PERMANENT MAGNET MOTORFiled April 15, 19 61 2 Sheets-Sheet 1 FIG. 2

FIG. I

JOHN L. BENNETT G] LB ER .WOOTTQN ROYAL LAGETT INVENTORS.

ATTORNEY P 1963 J. L. BENNETT ETAL 3,102,964

HIGH-EFFICIENCY PERMANENT MAGNET MOTOR Filed April 13, 1961 2Sheets-Sheet 2 JQHN L. BENNETT GILBERT B. WOOTTON ROYAL L. CLAGETTINVENTORS ATTORNEY 3,102,964 a HIGH-EFFICIENCYPERMANENT MAGNET MOTORJohn L. Bennett and Gilbert B. Wootton, Baltimore, and

Royal L. Clagett, Hampstead, Md., assiguors to The Black and DeckerManufacturing Company, Towson, Md., a corporation of Maryland Filed Apr.13, 1961,'Ser. No. 102,705

1 Claim. (Cl. 310-454) The present invention relates to ahigh-efticiencydirect current electric motor, and more particularly, to such a motorthat combines high-efiiciency with relatively high-output. i

It is an object of the present invention to provide a highefiiciencyhigh-outputdirect current motor which includes an encapsulated iron-freearmature having low mass, low inductance, and low windage. I

It is another object of the present invention to provide a highefiiciency high-output direct current motor having a stationarypermanent magnet concentric with the armature and disposed outwardlywith respect to the armature.

It is still another object of thepresent invention to provide a directcurrent motor having low frictional losses throughout.

It is yet still another object of the present invention to provide ahigh-efficiency direct current motor having a stationary ferrous corewithin a hollow cylindrical ironfree encapsulated armature.

These and other objects ofthe present invention will become apparentfroma reading of the following specification, taken in conjunction withthe enclosed drawings, in which:

FIGURE 1 is a longitudinal sectional view of the com pleted motor asmounted in a suitable frame;

FIGURE 2 is a sectional view taken along the lines 22 of FIGURE 1;

FIGURE 2a is an enlarged portion of FIGURE 2 showing the individualwires of the wound armature encapsulated within the plastic body ormatrix; and

FIGURE 3 is an exploded perspective, showing the main components of themotorv as viewed from a direction opposite to that of FIGURE 1.

In accordance with a specific embodiment of the present invention, ahigh-efliciencyhigh-output direct motor is provided having a frame whichincludes a pair of parallel side walls for purposesof mounting the maincomponents of the motor. Coaxially-aligned bearings are provided, one ineach of the walls; and an armature shaft is journaled in the bearings..A commutator structure is secured to the shaft also near one of thewalls, and

the shaft carries an iron-free armature" winding encapsulating andsupporting structure secured to the shaft adjacent to the commutator,preferably with both the armature winding-encapsulat-m'g structure andthe commutator structure integrally molded to each other and to theshaft by a continuous insulating plastic body or matrix. The armatureincludes a hollow cylindrical portion concentric with the shaft andprojecting axially away from the commutator in which the windings aresupported and encapsulated. A stationaryvtubular ferrous core issecuredto theother of the walls, and the core projects axially towardsthe commutator and is disposed within the hollow cylindrical portion ofthe armature. Both the core and the armature are concentric with respectto each other, there being a slight radial air gap therebetween. Thearmature shaft is in turn disposed concentrically within the tubularcore, there being radial running or operating clearance therebetween. Anouter concentric stationary permanent magnet is provided, which3,102,964 Patented Sept. 3, 1963 has a pair of diametrically-oppositesalient poles. The hollow cylindrical portion of the armature isdisposed between the poles of the magnet, being concentric with respectto the magnet; and the poles and the hollow cylindnical portion of thearmature have a-slight radial air gap therebetween. Thus, the coreserves to concentrate the magnetic flux passing through the hollowcylindrical portion of the armature and between the poles of thepermanent magnet; and the remaining portions of the magnet, between thepoles, provide circumferential return paths for the magnetic flux.

With reference to the drawings, the motor 10 is mounted in a frame whichincludes substantially parallel end walls 11 and 12. Wall 1 1 may bedeemed to be the ,fore wall, while the wall .12 may be deemed to be theaft wall. Respective bearings 13' and 14- are retained within, the walls11 and 12; and preferably, but not neces sarily, the bearings 13 and 14are of the needle type.

.A longitudinal shaft 15 of the armature (designated by the generalreference numeral 18) is journaled for rotation in the bearings 13 and14. The forward portion of the shaft 15 projects beyond wall 11, andconveniently a pinion 16 is, formed directly on the projecting portionof the shaft 15.. Shaft 15 carries a commutator 17 located near to thewall =11, and an encapsulated iron-free armature 18 (having windingsembedded in a plastic matrix) is carried by the shaft 15 and has aclosed portion 19 joined to the shaft 15 adjacent to commutator 17. Thearmature 118 further includes a main hollow cylindrical portion 20radially disposed with respect to the shaft 15 and projecting axiallyaway from the commutator 17 and towards the wall 11, and the hollowcylindnical portion '20 terminates in an integrally-molded collarportion 201:.

lt willybe appreciated from an examination of FIG- URES 1 and 3,- thatthe armature 18 including portions 19 and 20 thereof, together with thecommutator 17, shaft 15 and pinion 16, may be conveniently formed as asingle encapsulated subassembly, and that this overall subassemblycbnstitutes the only rotating component of the motor 10; moreover, themethod of windingthe coils of armature 1'8, together'with the process ofassembly and the molding technique, are more particularly described inthe co-pending Marshall application Serial No. 106,- 398 filed April 28,1961 (and assigned to the same assignee as the present invention. 7

Further, it will be appreciated that the hollow cylindrical portion 2 0and the commutator 17 are integrally molded or cast both with respect toeach other and to the shaft 15, and further that the motor 10 (with thepossible exception of the shaft 15) contains no iron or other ferrousmaterials in its rotating parts.- Furthermore, should it be desired, thearmature shaft-15 may be made of a non-ferrous material.

A stationary tubular core 21 is provided with a collar portion 22 seatedwithin a pilot counterbore 12a formed in the wall 12; and the collar 22is in turn secured to the side wall 12 by suitable means, such as aplurality of screws, one of which is indicated at 23. The core 21 isdisposed coaxially within and has a slight radial air gap with respectto the hollow cylindrical portion 20 of the armature 18. Moreover, core21 has a main tubular portion 24 which has a radial running clearancewith respect to the armature shaft 15, and at least the portion 24 ofcore 21 is made of a relatively-soft ferrous material. The motor 10 isfurther provided with an outer concentric cylindrical permanent magnet25, which may be made of 'Alnico or other well-known materials shownmore parthe co-pending Butler et al. application Serial No. 102,819,

filed April 13, 1961 and assigned to the same assignee as the presentinvention. This later referenced application is entitled.High-Efliciency Cordless Electric Drill and pertains to one type'ofelectrical device that the motor of the present invention finds aspecialutility. As shown more partieularly in FIGURES 2 and 3, the

permanent magnet 25 is provided with a longitudinalbore communicatepartially with thebore26, defining a pair of diametrically-oppositesalient poles 28 and-29, interrn/ediate the slots 27; and it'will beappreciated that each of the poles 28 and 29 has an arcuate face (shownas at 30 in FIGURE 3) coterrninous with the bore 26.

I It will also be appreciated that such a permanent magnet 25 usuallyhas a slidable keeper plug maintained withinthe bore 26 to insure thattherewill be no loss of magnetic flux'between the poles 28. and 29 instorage or transferof the magnet; and that in the assembly of the motor10, a'nd more particularly the permanent magnet ZSthereof, within atool-or device utilizing the motor 10', it is convenient (and wise) touse what may be deemed to be a transfer plug; Such a transfer plug, aswell as a keeper plug, are described in the aforementioned co pendingButler et all application Serial No. 102,819.

- As shown more particularly in FIGURE 2; the hollow V cylindricalportion 20 of the armature 18 is concentric-ally arranged between thepoles 28 and 29, there being a sli ght'radial air gap therebetween. Thusthe magnetic vflux, as shown by the dotted lines in FIGURE 2, will passbetween the poles 28 and 29 ofthe magnet 25 and through the hollowcylindrical portion 20 of the armature 18; These flux lines will beconcentrated by means of the stationary tubular core 21, while theportions 31 return pathiror the magnetic flux. I

Preferably, but not necessarily, the magnet 25 has an integral one-piececonstruction and is manufactured by means' known to one skilled in' theart.

Also, it will be appreciated from an examination of FIGURE 1, thatthe'rn-agnet 25 is substantially coterminous axially with I respect tothe hollow cylindrical portion 20 of therarmatu-dinal portions of thewindings, and that the integrally molded collar portion 20a has an axialrunning clearnet and the internal core for maximumefiiciency; live,

with relatively high-output. V The motor accomplishes these purposes inthe following manner; one, by reducing frictional losses throughout toan absolute minimum; two, by eliminating any magnetic material in therotating armature winding, thus considerably reducingthe usual corelosses that would otherwise be present; three, by 7 providing astationarypermanent magnet that is external to the armature, thusallowing a relatively large permanent magnet to' be used, andthus'maintaining a high air gap flux density for maximum power output;four, by providing a stationary tubular-ferrous core internally of the,

armature, the armature rotating between the external mags by making thearmature proportionally small in diameter in relation to the permanentmagnet; six, by providing an armature which has'low induotance, lowinertia, and at minimum windage; seven, by providing a low inertia rotating armature having consequently very low-massthus" presenting lowradial loads to the bearings, and. thus rev and 32 of the magnet 25 willprovide a circumferential ance both withrespect to the stationary magnet25 and to the collar 22 of the stationary core 21. Moreover, the core 21hasa sufficient axial running clearance with re spect to the closed endportion 19 of the armature 18; Also, asshown more particularly inFIGURE'1, some of themolding maten'al may extend from the closed portion19 of the armature 18- axiall'y or longitudinally around thearmatureshaft 15,-but this is for reasons of process or method ofassembly; and it is described more particularly invthe aforementionedco-pending Marshall application Serial No. 106,398. In FIGURE 1, theholders for the commutator-engagin'g brushes have been omitted for easeof illustration; but the brushes are conventional,

and for electrical considerations, may be made of silvergraphiteorcopper, if desired.

In summary, then, it will be appreciated that the teachings ofthe-present invention provide a direct current permanentmagnet'motorhaving high efficiency conjoined sulting in minimum frictional losses'inthe bearings; and eight, by utilizing an iron-free armature I windingstructure that is supported and-encapsulated by a body of insulatingmaterial integral with the commutator segment support and east directlyon the armature shaft;

We claim:

A h-igh-efiiciency.relatively high-output electric motor, comprising:

(a) ahousingcomprising'apairof substantially-parallel 7 Wallshavingrespective'bores formed therein and bearing-s in each of saidbores; (b) arotat-ing armature comp'risinga shaft journaled in saidbearings anda hollow cylindrical iron-free encapsulated portionintegrally-cast to said shaft'at one end of said armature, with saidarmature having an openradially-enl arged opposite end; (0)acornmuta'tor integrally-cast on the said one end of thearmature; a (d)respective windings in said armature, electrically connected to'said'comrnutator, and electrical brushes engaging said commutator;

('e) said one wall having an internal face having a pilot counterboreformed therein; I

(f) a stationary ferrous core comprising a tubular 'member open at bothendsand having an outwardlyiianged collar seatedwithin said counterboreand secured therein to said onewall;

(g) an outer stationary permanent magnet concentrically arranged withrespect to saidfh-ollow cylin-- dri'cal portion of said armature andsubstantiallycoterminous, axially, with respect to saidhollowcylindrical portion; I (h) said magnet, armature, andcore havingrespective radial runningclearances therebetween; (i) saidradially-enlarged portion of said armature beingdisposed between saidmagnet and said collar of said stationary core with respective axialrunning clearances therebetween; and

(i) said stationary core having an open'end, opposite a from its collar,confronting said integrally-cast portionof said armature with anaxi-alrunning clearance therebetWeen. j g

References :Cited the file of this patent UNITED STATES, PATENTSSteingger May 20, 1958 Hayes .1.. Nov; 11, 1958 2,978,598 Kato -i.'Apr.4,l9 6l

